Articles for adding manganese to aluminum

ABSTRACT

A method, articles and compositions are described for the direct addition of manganese metal to molten aluminum, which provide more rapid dissolution of the manganese in the aluminum that has been possible heretofore. The manganese is added to the molten aluminum in powder form (minus 14 mesh) in intimate admixture with a flux capable of forming a molten phase at the temperature of the molten aluminum to which the mixture is added. The flux, which is employed in an amount from about 3 to about 10 percent by weight of the total manganese-flux composition, contains chlorides other than those of manganese, fluorides and mixtures of such chlorides and fluorides; the preferred flux being 40 percent sodium chloride, 40 percent potassium chloride and 20 percent cryolite (Na3AlF6).

United States Patent [1 1 Kline et al.

[4 1 Feb. 11,1975

[ ARTICLES FOR ADDING MANGANESE TO ALUMINUM [73] Assignee: Foote MineralCompany, Exton, Pa.

[22] Filed: May 4, 1973 211 App]. No.: 357,256

Related U.S. Application Data [62] Division of Ser. No. 161,876, July12, 1971, Pat. No.

[52] U.S. Cl. 29/1912, 75/O.5 R [51] Int. Cl. B32b 5/16 [58] Field ofSearch..... 75/l34 M, 138,68 R, 44 R, 75/93, 0.5 R, 135; 29/l9l.2, I92

[56] References Cited UNITED STATES PATENTS 2,935,397 5/1960 Saunders etal 75/44 R 3,591,369 7/1971 Tuthill 75/138 Primary ExaminerR. DeanAttorney, Agent, or FirmHowson and Howson [57] ABSTRACT A method,articles and compositions are described for the direct addition ofmanganese metal to molten aluminum, which provide more rapid dissolutionof the manganese in the aluminum that has been possible heretofore. Themanganese is added to the molten aluminum in powder form (minus 14 mesh)in intimate admixture with a flux capable of forming a molten phase atthe temperature of the molten aluminum to which the mixture is added.The flux, which is employed in an amount from about 3 to about 10percent by weight of the total manganese-flux composition, containschlorides other than those of manganese, fluorides and mixtures of suchchlorides and fluorides;

the preferred flux being 40 percent sodium chloride 40 percent potassiumchloride and 20 percent cryolite |i)- 2 Claims, No Drawings ARTICLES FORADDING MANGANESE TO ALUMINUM This is a divisional of application Ser.No. 161,876 filed July 12, 1971 now U.S. Pat. No. 3,793,007 issued Feb.19, 1974.

BACKGROUND OF THE INVENTION Alloys of aluminum containing small amountsof manganese are widely known and used in the art and articles made fromsuch alloys constitute a large proportion of all wrought aluminumproducts. Alloys of this type, other than so-called master alloys,generally contain no more than about 1% percent of manganese by weight,although alloys containing up to 2 to 3 percent manganese may be usefulfor some purpose. Master alloys, which are intended to be dissolved inmolten aluminum to make ordinary manganese-containing aluminum alloys,may contain from about 4 to percent manganese. As a rule, however,lesser amounts of manganese, i.e., from 1 /2 percent down to as littleas about 0.01 percent are employed in commerical aluminum alloys. Forexample, type 3003 aluminum-manganese alloy, which contains from about1.0 to 1 /2 percent manganese, retains the high corrosion resistance ofpure aluminum, but has much greater strength than commerical purealuminum and also exhibits excellent forming and welding propertieswhich adapt it for use in a wide variety of applications, such as inaluminum foil and extruded shaped articles. Type 5056 manganese'aluminumalloy, which contains about 0.01 per cent manganese, is a well knownexample of the low manganese alloys.

The direct addition of manganese metal to molten aluminum is difficultdue to the fact that the melting point of manganese (1245C.) is muchhigher than the melting point of aluminum (660C). Moreover, the rate ofdissolution of metallic manganese in molten alu' minum is very slow. Asmight be expected, in general, the smaller the particle size of themanganese metal, the faster its rate of dissolution in aluminum. Forexam ple, manganese chips dissolve in molten aluminum more rapidly thanlarger lumps of the metal. Despite this observation it has notpreviously been feasible to pursue this advantage further with muchsmaller particles of manganese. This is due to the fact that whenmanganese in powder form is added to a bath of molten aluminum it floatson the surface and is sintered to a hard crust, with the result thatmuch of the manganese is oxidized and fails to be recovered as manganesemetal in the final alloy. For this reason powdered manganese haspreviously been added to molten aluminium chiefly in the form ofbriquettes formed from mixtures of powdered manganese with powderedaluminum. While such composite powdered manganese and aluminumbriquettes have provided better results than powdered manganese alonethey have not proven entirely satisfactory. Briquettes composedsubstantially entirely of manganese powder have been found entirelyunsatisfactory since they do not dissolve in molten aluminum.

In view of the above the usual means of adding manganese metal ofaluminum has been to prepare an aluminum-manganese master alloycontaining from about 4 to 30 percent manganese by weight. Such masteralloys have the advantage of dissolving relatively rapidly in moltenaluminum and also provide homogeneous distribution of the manganesethroughout the aluminum bath. Despite these advantages such masteralloys have presented handling and storage problems for both users andproducers and have the further disadvantage of being uneconomically highin cost. Therefore, a need has long existed for a simple, economicalmethod for adding manganese metal directly to molten aluminum in such away as to provide rapid dissolution of the manganese in the aluminum.

PRIOR ART In Austrian Pat. No. 211,559, which issued on Oct. 25, 1960,it has been suggested that alloying materials such as manganese beintroduced to light metal such as aluminum in the form of briquettescontaining pulverized alloying materials in combination with thechlorides of the alloying material and other chlorides, with or withoutthe-addition of a fluoride. More specifically, the suggested briquetteswould contain the pulverized alloying material in amounts equivalent to8 to 10 times the total chloride content. For alloying manganese with alight metal the briquettes would contain about manganese powder, about10 percent manganous chloride and about 10 percent of other chlorides,preferably 5 percent sodium chloride and 5 percent potassium chloride.Optionally, a fluoride capable of dissolving the deoxidation productsformed. during alloying may also be employed. lt is noted that manganouschloride is considered to be an essential ingredient of the briquettessuggested by the Austrian patent. Manganous chloride, being ahygroscopic material, tends to pick up sufflcient moisture from theatmosphere to cause excessively violent agitation of the molten aluminumbath and is, therefore, difficult to employ on a commerical scale.

Our co-worker, Jordan' P. Tuthill, in U.S. No. 3,591,369 issued July 13,1971 has suggested the direct addition of manganese metal to moltenaluminum in the form of a manganese body such as a chip having a coatingcontaining a potassium fluoride which forms a molten phase at thetemperature of the molten aluminum. Inasmuch as pure potassium fluoridemelts above 710C. the coating also contains at least one otherchemically bound element which lowers the melting point of the coatingand serves with the potassium and fluoride components to provide themolten phase. Such elements may be selected from the group consisting ofsodium, aluminum, manganese, titanium and zirconium, which metals arepreferably employed in the form of fluorides. While the Tuthill methodand composition have proven successful, and represents a definiteimprovement over the prior art, it would, of course, be desirable toprovide a method which would permit even more rapid dissolution of themanganese in the molten aluminum.

In view of the foregoing, it is apparent that despite significantadvances in the art looking toward the direct addition of manganese tomolten aluminum, a need remains for a method for accomplishing thisresult in a convenient and economical manner with improved rapidity ofsolution of the manganese in the molten aluminum and minimal loss ofmanganese.

It is, therefore, a principal object of the present invention to providea method to meet this recognized need in the art.

More specifically, it is an object of the present invention to provide amethod for the addition of manganese powder to molten aluminum withminimal loss of manganese due to oxidation of the powder and consequenthigh recovery of manganese metal in the final alloy.

It is another object of the invention to provide novel compositions andarticles for the direct addition of manganese metal to molten aluminum,which provide hitherto unattainable rates of solution of manganese inthe aluminum.

It is still another object of the invention to provide compositions andarticles which accomplish the foregoing objects in a convenient, safeand economical manner.

BRIEF SUMMARY OF THE INVENTION 'The'present invention provides a method,articles and compositions for the direct addition of manganese metal tomolten aluminum in such a way as to overcome the disadvantages of themethods of the prior art and provide previously unattainable rates ofdissolution of the manganese in the molten aluminum. The methodcomprises the addition of powdered manganese-flux compositions to moltenaluminum. The powdered manganese-flux compositions contain about 3 topercent of flux by weight of the total compositions, the balance beingessentially powdered manganese metal. The operable fluxes include thoseknown to the art which contain chlorides and fluorides or mixturesthereof which are capable of forming a molten phase at or somewhat abovethe melting point of aluminum, i.e., at 660C. up to about 710C. Themanganese-flux compositions are added to the molten aluminum bath inamounts to provide the desired concentration of manganese in the finalalloy, e.g., from about 0.l to 1.5 percent or up to 3 percent by weightof manganese in the aluminum alloy. Inasmuch as the manganese-fluxcompositions contain about 90 to 97 percent of manganese by weight, theamount of these compositions added to the aluminum is of about the sameorder of magnitude, although somewhat higher, (3 to 10 percent) than thepercentage of manganese desired in the final alloy.

The po'wdered manganese-flux additives may be handled in any suitableway for introduction to the molten aluminum. For example, a measuredquantity of the ad ditive may simply be added to the aluminum bathmanually, or a conventional vibratory feeder may be used to drop theparticulate material into the bath. Fore added convenience, the powderedadditive may be enclosed in a suitable consumable containter foraddition to the aluminum bath, e.g., a bag or envelope of aluminum foil,paper or a moisture proof laminate such as polyethylene-aluminumfoil-Kraft paper may be used. In another, but less preferred embodimentof the invention, the manganese-flux powder additive may be formed intobriquettes by conventional procedures and added in that form. While goodresults may be obtained in this way, it has been found that addition ofthe new compositions in free-flowing powder form provides more rapiddissolution of the manganese in the aluminum than in the compactedpowder form of the briquettes, probably due to the presence of a binder.

While the invention is especially useful for adding manganese directlyto the molten aluminum to provide alloys containing from about 0.1 to1.5 percent or up to 3 percent by weight of manganese, it may also beused to produce master aluminum alloys containing from 4 to 30 percentmanganese by appropriate adjustment of the amounts of the new additivecompositions or articles added to the aluminum bath, i.e., from somewhatmore than 4 to somewhat more than 30 percent by weight of the additive,depending on the concentration of manganese in the additive.

DETAILED DESCRIPTION OF THE INVENTION The manganese employed in theadditive compositions of the present invention may be derived from anyknown source according to known techniques, such as by thepyrometallurgical reduction of ore, or by electrolysis. Electrolyticmanganese is preferred, however. The manganese metal is reduced to theform of a freeflowing powder by known grinding techniques. When usingelectrolytic manganese, such as chips of the metal formed by breakingmanganese away from the cathode on which it has been plated, it ispreferred to remove any adherent electrolyte by washing, suitablechemical treatment, or both.

The powdered manganese-flux additive compositions of the invention maybe formed by simply mixing the powdered manganese and dry flux materialsin conventional mixing apparatus to obtain a dry, free-flowing powder.It is not essential, however, that the flux be in powder form and ifdesired the powdered manganese may be incorporated in a cake ofagglomerated or fused flux.

While the particle size of the manganese powder may vary widely, it ispreferred that it be essentially minus 14 mesh, and primarily plus I00mesh. By this it is meant that substantially all of the manganeseparticles will pass through a standard 14 mesh screen and be retained ona standard mesh screen. While it is, of course, desirable that theparticle size of the manganese metal be relatively fine, i.e., minusabout 14 mesh, in order to promote rapid dissolution in the moltenaluminum, it is preferred that no more than about 20 percent by weightof manganese particles be minus 100 mesh, in order to prevent unduelosses of manganese in the final alloy due to oxidation of such fines.The distribution of particle sizes within the stated range is notcritical and various distributions of particle sizes within the aboveranges have been found to be entirely suitable. For example, specificpowdered manganese additives have been tested containing manganeseparticles of (l) substantially all minus 30 mesh and plus I00 mesh; (2substantially all minus 30 mesh and smaller; and (3) substantially allminus 20 mesh and smaller, all mixed with about 10% by weight of fluxbased on the total additive compositions.

The amount of flux required for best results depends to some extent uponthe particle size of the manganese powder employed; the finer themanganese powder, the more flux required to prevent its oxidation. Ingeneral, if the particle size of the manganese powder is in the rangefrom about minus 14 mesh to plus 100 mesh, or minus 14 mesh and smallerwith no more than about 20 percent minus 100 mesh, about 3 to about 10percent of flux, by weight of the total additive compositions isemployed. From these general considerations, those skilled in the artwill be able to select an appropriate flux concentration within theabout 3 to about l0 percent range, or at somewhat lower or higherconcentration levels for larger or smaller mesh manganese particles,respectively.

The fluxes, as noted above, are chlorides or fluorides, or mixedchlorides and fluorides, and which are capable of forming a molten phaseat the temperature of the molten aluminum to which the manganese-fluxcompositions are added in order to aid in the wetting of the manganeseparticles by the aluminum and thus facilitate solution of the manganesein the aluminum. Suitable fluxes include those described in the TuthillU.S. Pat. No. 3,591,369 issued July l3, 1971, the disclosure of which isincorporated herein by reference. As noted in that application,potassium fluoride which is an excellent flux, has a melting point ofabout 710C. and, therefore, when it is desired to alloy aluminum at atemperature below 710C., but above the melting point of aluminum (660C)it is necessary to lower the melt ing point of the potassium fluoride bythe addition of another chemically bound element. Suitable materials forthis purpose include the chlorides and the fluorides of sodium,aluminum, titanium and zirconium, and manganese fluoride. Manganouschloride is not desirable in a flux for aiding the dissolution ofmanganese in molten aluminum since, due to its hygroscopic nature, itnormally carries with it sufflcient moisture to cause unacceptablyviolent agitation of the molten aluminum bath. The chemical identity ofthe flux is not critical so long as it is capable of forming a moltenphase at the temperature of the aluminum bath and also serves to aid inthe wetting of the manganese particles by molten aluminum. Suitablefluxes include MgF K ZrF KF,AlF LiF, Zl'FqKCi, LiCl, MgCl ZnCL, andmixtures of these salts. While K- TiF is a particularly suitable flux itis more expensive than the preferred flux of the invention, whichconsists of a mixture of KCl, NaCl and cryolite. An especially preferredflux consists of40 percent KCl, 40 percent NaCl and percent cryolite(Na;,AlF,6).

The invention will now be described in greater detail in relation to therelative rates of solution of manganese metal in molten aluminumattainable with the method, articles and compositions of the inventionas compared with those of the prior art.

EXAMPLE 1 A series of laboratory experiments were carried out in whichvarious manganese-containing additives were introduced to a bath ofmolten aluminum maintained at 746C. (l375F); the amount of manganese ineach additive being equivalent to 1.25 percent of the weight of themolten aluminum bath. Analytical samples were withdrawn from the moltenaluminum bath at various intervals until 95 percent of the manganese wasdissolved or until a maximum time of 84 minutes. These samples wereanalyzed for manganese dissolved in the aluminum bath and the calculatedvalues of the percentage of the manganese in each additive which haddissolved were plotted against time. The time in minutes for each sampleto reach percent. 50 percent, 75 percent and 95 percent dissolution ofmanganese were then read from these curves, and set forth in Table lbelow.

TABLE I Time in Minutes Required to Reach Mn Dissolved TABLE l-ContinuedTime in Minutes Required to Reach Mn Dissolved Type Mn Added 25 50 MnChips 32 Hr. Electrolytic 3.50 7.50 l3.50 22.25

Mn Chips Coated w/ K TiF,

16 Hr. Electrolytic 1.50 2.75 4.25 9.50

Mn Chips Coated w/ KgTifq *Did not reach 95% dissolved during the 84minute test. The manganese powder was substantially all minus 30 meshand plus l00 mesh and the flux consisted of 40% KCl. 40% NaCl and 209?cryolite.

EXAMPLE 2 In order to evaluate the manganese powder-flux articles andcompositions of the present invention with re spect to those of theprior art, a series of tests were carried out according to the followinggeneral procedure.

SOLUTION RATE TEST PROCEDURE Aluminum (400 lbs.) is melted in an ironpot, heated to 746 C. and maintained at that temperature throughout thetest procedure. Any dross present on the surface of the molten aluminumis removed by skimming. The samples of manganese-containing additivesare added directly to the molten aluminum. Powder mixtures were enclosedin a polyethylene-aluminum foil- Kraft paper bag and the entire bagdropped into the aluminum bath. Briquetteed mixtures were removed fromthe trilaminated bags and added to the aluminum bath with a shovel. Thebriquettes are made by mixing 10 ml ofAcrysol 6-1 10 (an ammoniumpolyacrylate solution available from Rohm and Haas) as a binder in 20 mlof water with the bulk (2551.8 to 2807 g.) of the mixture to bebriquetted and compressing the resulting material into briquettes at15,000 psi. The mixed or briquetted products are immediately sealed inpolyethylene-aluminum foil-Kraft paper bags to prevent those which arehygroscopic from picking up water from the atmosphere. After addition ofeach sample of additive to the molten aluminum bath 0.2 lb. samples ofliquid metal are removed from the bath at the end of l, 3, 6, 9, l4, l9,24 and 34 minute intervals. The samples are then analyzed for manganesecontent by X-ray fluorescence according to known techniques and thepercentage of dissolved manganese in the bath is calculated. accordingto the formula: X(l) =(C(L)*(A+ t ML*S)+S*Cl /M I sample number X(l)dissolved of the lth sample C(I) Mn of the lth sample A weight of Al Mweight of Mn S weight of the liquid metal sample Cl sum of the manganesefor all samples up to and including the lth sample m ultiplication whichis percent by weight of the manganese-KC] -NaCl-cryolite mixture. Theproportions of KCl:NaCl:-

cryolite in this flux are 40 percent; 40 percent; percent, respectively.Some of the compositions also contained 255.2 g. of MnCl as recommendedby the Austrian patent referred to above. Some of the compositions werebriquetted as described above while some were used in the form of thefree-flowing powders. 1nasmuch as the degree of agitation is a factor inthe dissolution of manganese in molten aluminum, the effect of thisfactor was also evaluated by stirring some of the samples and notstirring others. The samples tested are listed by identifying codenumber and described in table 11 below.

I Table 11 Charges and Variables The percentage of the originalmanganese content of each additive sample of table 11 dissolved in themolten aluminum bath at the end of specified time periods during thetest procedure is set forth in table 111 below.

' Table 111 It was observed that all of the samples containing MnClcaused such violent agitation of the bath of molten aluminum that moltenmetal actually bubbled out of the pot. While this bubbling aided inraising the solution rate of manganese in the unstirred melts due to thestirring action of the bubbling, such violent bubbling would not beacceptable in commerical practice. The powdered manganese-fluxcompositions of the present invention, on the other hand, did notagitate the melt significantly. The stirred melts containing MnCl showedlittle improvement over the unstirred melts also containing MnCl It isapparent that the usual commerical practice of stirring the melt isnecessary with the articles and compositions of the invention. It isnoted, however, that with stirring, the briquetted articles of theinvention were superior to the briquetted Mncl -containing articles ofthe prior art, since they achieved 95.2 percent manganese recovery ascompared to only 77.6 percent recovery for the MnCl -containingarticles.

The best results, however were achieved by the preferred free-flowingpowder manganese-flux compositions of the invention which achieved 100percent manganese recovery as compared to only 83.2 percent recovery forsuch compositions also containing MnCl It is clear, therefore, that MnClis detrimental to the recovery of manganese metal in aluminum alloys andthat its use also presents safety hazards.

While the invention has been described in conjunction with certainspecific embodiments it is to be understood that these are merelyillustrative of others which will be apparent to those skilled in theart.

Percentage of Manganese Content of Additive Dissolved in Molten AluminumBath Sample Time in Minutes 48 A 17.6 77.6 83.2 84.8 82.4 84.0 83.2 83.2B 3.2 100.0 100.0 100.0 100.0 103.2 99.2 100.0 49 A 8.0 36.4 93.6 95.96.0 95.2 97.6 95.2 B 55.2 72.8 76.0 73.6 74.4 74.4 74.4 78.6

Further analyzing the results of this series of tests. the percentagesof manganese recovery, i.e., percent of manganese from the additivefound in the samples of liquid aluminum alloy, by each of the variablesMnCl present or not, powder or briquette, and stirred or not stirred,are set forth in table 1V below.

Table IV Percent Manganese Recovery by Variable MnCl PowderBriquette-Stirring A. No Stirring MnCl 62.4 71.2

I MnCl 12.0 22.4

B. Stirring MnCl 83.2 77.6

MnCl 100.0 95.2

2. An article according to claim 1 wherein the flux contains about 40percent sodium chloride, about 40 percent potassium chloride and about20 percent cryolite.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. I3,865,584 Dated February- 11. 1975 James D. Kline, 7 William C. T.- Yehand Inventofls) Ulvsses A. Preston It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column-1 2; line 21, "so" should read 80% Column 3, line 46, "Fore'v'should read For Column 5, line 26, ".ZrF KCl" should read ZrF .KCl u--,and "ZnCl should read ZrCl Column 5, line 27, "K TiF should read K' TiF-Q Column 5,- line 32', "(Na AlF 6)" should read (Na AlF- Column6, lines58 and 59, both places, '-'L" in the formula should read. I.

Column 6 line 71, before "and 51.0 g" should read 102.1 g

of NaCl Signed and Scaled this fourth Day Of November 1 975 KSEAHArrest:

RUTI'I C. MASON C. MARSHALL DANN Anming Officer (ummllsriuner ufParemsand Trademarks FORM PC4050 (1M9) USCOMM-DC 503764 69 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,865,584 DatedFebruary. 11, 1975 Q James D. Kline, William C. T.- Yeh and Inventor(s)UlVsseS A. Preston It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

eel-me, line 21, "so" should read 80% Column 3, line 46, "Fore'.' shouldread For Q Column 5, line 26, "ZrF KCl" should read ZrF .KCl

and "'ZnCl should read ZrCl Column 5 line 27, "K TiF should read K TiFColumn 5,-line 32, "(Na AlF 6)" should read (Na AlF- Column 6, lines 58and 59, both places, in the formula should readv I. h

Column 6, line 71, before "and 51.0 g" should read 102.1 g of NaCl I o IQ Signed and Scaled this fourth Day Of November 1 975 ISEALE Arrest:

RUTH C. MASON C. MARSHALL DANN M /1 Commissioner nj'Parenl: andTrademarks FORM POH lM-GQ) USCOMM-DC scan-ps9

1. AN ARTICLE COMPRISING A CONTAINER CONSUMABLE IN A BATH OF MOLTENALUMINUM CONTAINING A PREDETERMINED QUANTITY OF A COMPOSITION CONSISTINGESSENTIALLY OF ABOUT 90 TO 97 PERCENT OF FINELY PARTICULATE MANGANESEMETAL AND ABOUT 3 TO 10 PERCENT OF A NONHYGROSCOPIC METAL SALT FLUX,BASED ON THE WEIGHT OF THE TOTAL COMPOSITION, SUBSTANTIALLY ALL OF SAIDMANGANESE METAL BEING MINUS 14 MESH AND SAID FLUX FORMING A MOLTEN PHASEAT THE TEMPERATURE OF MOLTEN ALUMINUM TO WHICH SAID COMPOSITION ISADDED.
 2. An article according to claim 1 wherein the flux containsabout 40 percent sodium chloride, about 40 percent potassium chlorideand about 20 percent cryolite.